Recent increases in crack injection and associated risk factors among people who inject psychoactive drugs in England and Wales

Background: Crack use is higher in the United Kingdom (UK) than other European countries. Crack is a stimulant with a short half-life, requiring frequent injection to maintain its euphoric effects, thus increasing the risk of blood borne viruses (BBVs) and skin and soft tissue infections (SSTIs). We assessed trends in the prevalence of current crack injection among people who inject drugs (PWID) and investigated harms and other factors associated with its use. Methods: We used data from the annual Unlinked Anonymous Monitoring Survey of PWID, which recruits people who have ever injected psychoactive drugs through specialist services. Participants provide a biological sample and self-complete a questionnaire. We included participants from England and Wales who had injected in the past month. We examined trends in crack injection over time (2011–2021) and factors associated with crack injection using multivariable logistic regression (2019–2021). Results: The proportion of people self-reporting crack injection in the past month almost doubled between 2011–2020/21, from 34 % (416/1237) to 57 % (483/850). Crack injection was more frequently reported by males than females (adjusted odds ratio 1.46, 95 % confidence interval: 1.15–1.87) and injected alongside heroin (6.67, 4.06–10.97) more frequently than alone. Crack injection was independently associated with injecting equipment sharing (1.64, 1.30–2.07), groin injection (2.03, 1.60–2.56) in the past month, overdosing in the past year (1.90, 1.42–2.53), homelessness in the past year (1.42, 1.14–1.77) and ever having hepatitis C infection (1.64, 1.31–2.06). Conclusion: Crack injection has increased significantly over the past decade in England and Wales. People injecting crack are more likely to engage in behaviours that increase the risk of BBV and SSTI acquisition, such as needle/syringe sharing, groin injection and polydrug use. Harm reduction and drug treatment services should adapt to support the needs of this growing population of people injecting stimulants.